Importantly, the PSA−/lo PCa cell population is heterogeneous harboring and/or overlapping with other tumorigenic subsets including the SP, holoclones, and ALDH+, CD44+, α2β1+, and ABCG2+ cells [6–8, 10, 12, 13; this study] (Figure 11) and, likely, other subsets such as CD133+ [15] and TRA-1–60+CD151+CD166+ cells [19], which are AR−PSA−. Here, ABCG2 is linked to posterior cortical atrophy.